This invention generally relates to communication systems such as TVRO's for the reception of audio and/or video transmission signals broadcast from a plurality of orbiting earth satellites. More particularly, the invention relates to a earth-station antennas and techniques for accurately positioning them for the reception of signals broadcast on one or more channels by geosynchronous orbiting satellites, for reproduction on TVRO's or similar systems.
In satellite communication systems, a transmitting earth station generates a modulated carrier in the form of electromagnetic fields up to a satellite, forming an "uplink". The incident electromagnetic waves are collected by the satellite, processed electronically to reformat the modulated carrier in some way, and retransmitted to receiving earth stations, forming "downlinks." The earth stations in these systems basically consist of a transmitting and/or receiving power station functioning in conjunction with an antenna subsystem and form strategic parts of the satellite communication system.
In earth stations, particularly the receive-only type such as TVRO's, the antenna and the way in which its orientation is controlled plays a very important role especially with the rapidly increasing number of orbiting satellites being positioned in today's communication satellite systems. Antennas for receive-only earth stations, such as conventional TVRO systems, have to be extremely directional and must be capable of being oriented with increasing accuracy in order to track and differentiate among signals from satellites that are spaced increasingly closer together. Misorientations of the order of even fractions of a degree can mean the difference between perfect reception of a required channel and total loss of reception altogether. This makes manual positioning of earth-station antennas extremely bothersome and inaccurate.
The increased positional accuracy also has to be complemented with simplicity and convenience in locating orbiting satellites; especially so because of the rapidly increasing number of private individuals or consumers using TVRO systems to receive television transmissions directly from orbiting satellites. The projection of TVRO systems or similar compact earth station terminals into the consumer electronics market has raised the need for an efficient satellite-seeking technique for antennas used with such systems, which is together simple, fast, accurate and, in particular, lends itself easily to automation so that the end user can conveniently control the antenna sub-system to receive the channel of his choice from any commercially broadcasting orbiting satellite.